Cyclic method for removal of impurities from coke oven tar by water washing



A. N. HELLER ETAL CYCLIC METHOD F'OR REMOVAL OF IMPURITIES FROM May 17, 1960 COKE OVEN TAR BY WATER WASHING Filed June 24, 1957 4 Claims. (Cl. 208-39.)

This 'invention relates Vto an improved method for :ex-

tractingwater-soluble salts from water-immiscible liquids,

and more particularly refers 'to a new and improved method of carrying out `the removal of 4chlorides from heavy coke oven tar.

Coke oven `tar is a vaporous product resulting from the destructive distillation of co'al. In the rening of coke oven tar, the crude tar is initially condensed from coal gas and flushed from gas -mains by recirculfated NH3 liquor. Crude condensed `tar and NH3 'liquor pass to ltar and liquor decanter tank, `where solid sludge settles out'. Tar yand liquor go to a storagetank where ltar liows under a Weir to a tar overflow tank, thence fto `a Atarstorage tank. The semi-finished tar, also '-termed crude tar, invariably contains some liquor.

' It fis essential fthat wet tars be dried before the distillation step in refining for lproduction 'of finished tars vsince `the ammonium chloride in the aqueous liquor 'would otherwise plug up condenser tubes and causefsevere -cor rosion to still bottoms. Also excessive moistureparticularlyfin the form of Aslugs of water results in violent bumpin-g duringV distillation, with result-ant vdanger to operating personnel as well as poort heat economy fand malperformance of the unit. Removal of excess aqueous liquor is therefore an essential preliminary to safe, controllable and economical tar refining.

Y `-Conventional methods of removing ammoniumchloride from tar are based on long settling of the tar at elev-atcd temperatures in an effort to cause `settling out vof chloride containing water, or on adding water in small amounts and fseparation of the yaqueous phase by Vsuch means i'as-centrituging. These methods have proven coste ly Iand time consuming, andin the case of'heavy tar khaving -a specific gravity at 25/25va C. above 1.10, ineiective to reduce the chloride and water content to a satisfactorily low lim-it -due to the presence of lliquor 'occluded by the heavy coke loven tax as a Water-in-'oil emulsion. While it is important to reduce vthe chloride content 'of coke oven tar to below two 4pounds per 1,000 gallons of tar and of 'water to below 2% by volume of the coke oven tar in a "rapid, economical and 'efficient method, in addi# tion, it is important to accomplish this vresult without creating a pollution problem Iand with a minimum consumption of water, which is expensive and in certain locations a -scarce commodity, 'and also to effect recovery of waste phenolics and ammonium chloride.

One object of the present invention is to `provide an eilicient, economical methodof reducing thefehloride contentoll thecoke oven tar (measured as NHtCl) v'to below two 'pounds 'per 1,000 gallons oftar and the Water content ojf the tar to below 2% by volume lof the tar.

Another object of the present invention is to provide a method of reducing the chloride and water contents of coke oven 'tar to a low level of concentration employing asmall :amount of water for eiiecting same.

A further object of the present invention is to providev a .method for reducing the `ammonium chloride content and water content of coke oven tar to a low level of ICC concentration -which avoids pollution `with waste `-vcfater fand permits recovery fof phenolics vand la'mrrionium "chloe ride. Otherfo'bje'cts 'and advantafges lwillfbe apparent from the 'following description tand accompanying drawing. 'j

In vaccordance with the present invention, '-eicient, economical reduction of ammonium chloride to Jbelow 'two pounds per 1,000 gallons of tar and -oifwatergto 'below .2% by volume Aof tar, with concomitant production `o'f 'an aqueous solution containing phenolics and ammonium v'chloride adapted for recovery of 'thephenoli'cs `Iandam- Vmonium chloride, may be accomplished by` vcontacting crude coke oven tar containing unsep'ara'ted ammoniaca'l liquor, i.e.loecluded'aqueous liquor having dissolved'there- 'in ammonium chloride and phenolcs, particularly Aheavy crude 'coke oven ftarlof 'a 'speciiic gravity at '2S/,25 lC. rabove 1.14 'and a float test 'above '80"seconds at '32 "F., 'with a mixture containing agmajor portion of recycled aqueous -solution `and a minor portion of make-up *water in the proportion of "0.6-2.0, preferably '0.8-'1.3 volumes aqueous mixture -to one volume of lcrude coke Joven tar, effecting intimatecontact -between the coke oven 'tar and aqueous liquor, heating said mixture 'of tar and aqueous 'liquor -to a temperature between 180.and 350 F., `preferably Z50-350 F., and under sufficient pressuretojprevent rsubstantial -vaporization from the mixture, effecting separation of the mixture of heated coke oven tar and aqueous liquor into two phases by 'settling at 'a temperature within the -r'ange of 180-350 F., preferably 2504 350 F., 'under suilicient pressure to prevent 'substantial vaporizat'ion into an aqueous layer, and atar layer, pre`- erably effecting said 'settling "by flowing the 'mixturesu`b Vstantially horizontally through ,a substantiallyhorizontal# ly disposed settling section and thence `into a vertical settling section, withdrawing the 'tar layer and subjecting it vto reduced ,pressure `to `effect ilash vaporizat'ion of a small amount of volatile aqueous kconstituents contained therein, discharging 'the coke oven tar 'having a low level of concentration of Vammonium chloride and waterfin .an amount Vof less than two pounds ammonium chloride .per 1,000jgallons tar and less than 2% Water by volume of tar, condensing vapors evolved by said ilashvaporization of the tar, preferably passing said vapors in --indircct contact with crude `coke oven feed tar to preheat .said crudeV feed tar and to 'condense said vapors,y .returning said :condensate for .contact with incoming crude .coke ovenV tar, recirculating aqueous layer for further contact with crude heavy coke oven tar, preferably rst passing the recirculated layer in indirect heat exchange with. incoming crude coke oven tar, discharging a .small amount, vabout 5`2`5%,V preferably 1`0-20%, of the recirculating aqueous liquor, introducing about A5-25%, preferably `1-0 20%, make-up Water by volume of recirculating :liquor in admixturejwith the circulatingk -aqueous liquor sufficient to maintain the amount of circulating liquor substantially constant.

The accompanying drawing lis a diagrammatic flowisheet Yillustrating one method of practicing the present'invem tion.

Referring to the drawing, lcrude or semi-finished tar produced by high temperaturecar'bonization of coal baving a specic gravity Within the range Aof 1.1-1.30, particularly above 1.14 and a iioat -test above seconds' at 32 F., containing from 5 to as` much as .25,Y pounds ammonium chloride per 1,000 .gallonsof tar and from 4 to 20% by 'volume water, whichlatter hasa pheno1ics,.,a mixture fo phenol and homologues'ofphenolycontent of 15,000 to 20,000` ppm., enters Vthrough line 1, ,flows through condenser 2 wherein it passes in indirect contact with ash vapors r'entering condenser l2 throughflinefZfand discharging through lline 4 thereby condensingfthe vapors and'transferring heat to thecrude colte oven feed tar leaving condenser 2 through line 5. The preliminarily -changer 6 through line 9 into crude tar storage tank 11 which, if desired, may be provided with heating means such as a steam coil, not shown in the drawing, to preheat the crude tar. Crude tar at a temperature of from 60 to about 200 F. is withdrawn from storage tank 11 through line 12 and directed by pump 13 through line 14, ow controller 15 and line 16 into mixing tank 17 provided with a high speed propeller-type mixer 18. Aqueous liquor flowing through line 19 and ow controller 21, or line 22 and ow controller 23, is admixed with the tar in mixing tank 17. Crude heavy coke oven tars are capable of holding Water in excess of 12% of the weight of the tar vin stable water-in-oil emulsions, and this kind of aqueous solution does not easily settle out to a sufficient degree to etect a high degree of removal of ammonium chloride from the tar. One of the factors important to achieve effective removal of ammonium chloride is contacting the tar in mixing tank 17 With-0.64.0, preferably 0.8-1.3, volumes aqueous liquor per volume of tar. This, coupled with intimate mixing, prepares the mixture of tar and aqueous liquor for separation of the aqueous phase from heavy tar to produce a tar of low ammonium chloride and low water content. The high speed propeller-type mixer effects intimate mixing of the tar and aqueous solution such that the ammonium chloride occluded within the tar is transfererd to the aqueous solution. This transfer occurs when -microscopic thin films of tar are formed in contact with the aqueous solution through shearing actionaccompanied by mechanical mixing. Flow control- 1ers 15, 21 and 23 are set to maintain the volume of tar pumped to mixing tank 17 from tar storage tank 11 in the desired proportion of one volume tar to 0.6-2.0 volumes aqueous liquor entering mixer 17 through lines 19 or' 22.

It is obvious that the lower the quantity of aqueous solution remaining occluded in the wash tar after recovery of a separate aqueous phase, the less will be the chloride content of the washed tar. It follows that reducing the amount of aqueous solution in the washed tar permits increasing the average ammonium `chloride content of the recycled aqueous solution and ythereby reduces the bleed stream of aqueous by-product. It therefore follows that clective separation of the contacted phases to achieve a minimal concentration of aqueous solution in the washed tar phase is an important step in the process.

Separation of the aqueous liquor may be accomplished by withdrawing the contents of mixing tank 17, subjected to agitation by high speed propeller-type mixer 18, through line 24 and thence by means of pump 25, raised to superatmospheric pressure and pumped via line 26, through flow controller 27 to tar heater 28 wherein the mixture is heated to a temperature of ISO-350 F. Although the mixture of aqueous liquor and tar may be heated to a temperature of about 180-200" F. under atmospheric pressure, subsequent separation of such mixture under the conditions requires a long time, particularly for heavy tars having a specic gravity above 1.14. Consequently, it is desirable to heat the mixture to a temperature within a range of about 250-350 F. and under sufcient superatmospheric pressure, generally in excess of 50 p.s.i.g. and below 250 p.s.i.g., to prevent vaporization of the volatile constituents of the mixture and to effect separation under the conditions. The heated mixture of tar and aqueous liquor discharges from tar heater 28 through line 29 and pressure'` regulator 31 into continuous settler 32. An economically sized settler, designed. as illustrated by continuous settler 32, operating under superatmospheric pressure, is composed of a horizontal portion 33 and a vertical portion 34.

' The purpose of the horizontal portion is to effect preliminary settling of phases accompanied by Vslow forward 110W, which tiow prevents stratification of droplets of one phase within the other phase, and aids the small droplets to coalesce and thereby more rapidly migrate out of the opposite phase. settler should have at least as large or larger cross-sectional area as the horizontal section in order to prevent turbulence occurring at therunion of horizontal and vertical sections of the settler.

The tar phase settles out in the vertical portion 34 of continuous settler 32, passes through line 3S, ow controller 36, pressure reducer 37 into flash drum 38 maintained at a lower pressure wherein further reduction of tar Water content is accomplished by flash evaporation and the llash vapors released from the top of flash drum 38 through line 3. Product tar, substantially free of ammonium chloride and water, is withdrawn from the bottom of ash drum 38 through line 41 and sent through line 42 to storage. The use of flash dehydration by release of pressure is particularly advantageous in the treatment of heavy tars which resist complete separation of water from the tar in the settler. Further, the use of flash evaporation in conjunction with the continuous settler speeds up the operation and permits the use of smaller size settling equipment, in that complete separation of the water may not be accomplished in the settler but may be effected in ash drum 38 in a much more rapid and expeditious manner. For lighter tars wherein separation of the aqueous phase from the tar is quite complete and tar may be sent directly through lines 43 and 42 to storage, separation of the aqueous phase from the tar in settler 32 may be rapidly accomplished, in a matter of 10-60 minutes.

The aqueous phase passes up Ithe vertical section 34 of continuous settler 32 via line 46,- through ow controller 47, thence lthrough line 7 where it is cooled by countercurrent contact with crude feed tar in heat exchanger 6 and then passes through pressure regulator 10 in line 8, thence through lines 48 and 49 to liquor decenter tank S1, or through lines 43 and 52 into alternate liquor decanter tank 53. In some instances the aqueous phase contains small amounts of crude tar, generally less than 1% suspended in the liquor. In these circumstances, the liquor is sent via lines 48, 49 and 52 to alternate liquor decanter tanks wherein settling of the small amount of tar in the liquor occurs. In this manner, a small amount of clarified liquor, about 5-25%, preferably l0-20% by volume of the recirculated liquor, may be withdrawn from tank 51 through line 54 and from tank 53 through line 55 and sent by pump 56 for recovery of ammonia and phenolics. Aqueous liquor, recirculating through line 48, requiring no additional clarication, may be sent directlytov mixing tank 17 via lines 57v and 19 -or only one liquor decanter tank need be employed. Also a small amount of recirculated liquor may be bled off Ifrom the stream owing through line 48 and discharged through lines 58 and 54 for recovery of ammonia and phenolics. To compensate for the withdrawal of product liquor, make-up water is introduced into the circulating system through lines S9 and 61 joining the stream of recirculated liquor tlowing through line 48, or through lines 62 and 63 into liquor decanter tank 51, or through lines 62 and 64 into liquor `.decanter tank 53. Thus by recycling aqueous liquor over and over again with only a small bleed olf and the addition of a small amount of make-up water, there is accomplished reduction of the ammonium chloride content of the tar to a value -below two pounds per 1,000 gallons tar and reduction of water content to below 2% by volume with consumption of only a small amount of make-up Water and the production of a small amount of liquor which contains phenolics and ammonium chloride in sufficient concentration to'permit recovery therefrom and eliminates a waste disposal and pollution problem. Liquor from tanks 51 and 53 is sentv via lines 65 and 66 and line 67 by pump 68 through lines 69, 19 and low controller 21 into mixing tank 17. Settled tar from the bottom of The vertical section of the continuousv phenolics, `and ammonia.

`tanks 51er 53is 'likewise j-pmnpedzv'ia lines T11-i772,

4by pump 74 through line 22 and ftlow controller 23 into mixing tank 17.

The following examples yillustra-te the presentinvention.:

Example l ymixture of Ytar and aqueous liquor 'was heated `to i304` F.

and introduced into the continuous settler 'under superatmospher-ic pressure of '140 p.s.i.g. The residencetime in the settler was 19.8 minutes. The aqueous layer was recirculated lto .the liquor decanter tank wherein, together with make-up water,l .the mixturewas further contacted with additional crude coke oven tar. An amount of aqueous liquor, about equal Vto the amount of make-up water, was discharged 4from the system tor recoveryofl The tar withdrawn `from the continuous settler contained 0.73 pounds ammonium chloride per 1,000 gallons of A.tar and about 2% water. Passagel of thetar to a flash Ydrum further reduces the water content of the tar.

Example 2 Another batch of 16,000 gallons of crude coke oven tar was collected in the crude tar storage tank. This tar was a heavy tar similar to the heavy feed tar of Example 1 but having 14.2 pounds ammonium chloride per 1,000 gallons of tar and three volume percent water. The operation was similar to that of Example l, differing principally in that the composition ofthe liquor was 86% recirculated liquor and 14% make-up waterv and the residence time in the continuous settler was 28.2 minutes. The coke oven tar product, after passing through the liash drum, contained 0.9 pounds ammonium chloride per 1,000 gallons tar and 2.0% water.

Although certain preferred embodiments of the invention have been disclosed for purpose of illustration, it will be evident that various changes and modifications may :be made therein without departing from the scope and spirit of the invention.

We claim:

l. A process for the treatment of crude coke oven tar containing unseparated ammoniacal liquor, i.e. occluded aqueous liquor having dissolved therein ammonium chloride and phenolics, for reduction of ammonium chlo- Iride to -below two pounds per 1,000 gallons of tar and of ovenltarlhavinga low concentration of ammoniumclilo- 'ride and Water, recirculating .aqueous layer as aqueous liquor for further contact with `crude heavy coke oven n tar, discharging a small amount, about 5,--'25%, of the recirculating aqueous liquor, and introducing about 5-25% make-up water by volume of circulating lliquor in .admixture with the circulating aqueous liquor sucient to maintain the amount of circulating liquor substantially constant.

v'ride and phenolics, for reduction of ammonium chloride to ibelow two pounds per 1,000 gallons of tar and of water to below 2% by volume'of tar with concomitant .production of an aqueous solution containing phenolics and ammonium chloride adapted for recovery of the phenolics and ammonium chloride which comprises continuously recirculating aqueous liquor vin a closed circuit m which a mixture of the aqueous liquor with a `minor proportion of make-up water is intimately contacted with crude coke oven tar having a specific gravity at 25/25 C. above 1.14 and a float test above 80 seconds at 32 F. in the proportion of 0.8-1.3 volumes yaqueous mixture 'to one volume of crude coke oven tar, heating said mlxture of Vtar and aqueous liquor to a temperature be- 'tween 250 and 350 F. under suflicient superatmosph'eric ,pressure to prevent vsubstantial vaporization from the mixwater to below 2% -by volume of tar with concomitant production of an -aqueous solution containing phenolics and ammonium chloride adapted for recovery of the phenolics and ammonium chloride which comprises continuously recirculating aqueous liquor in a closed circuit in which a mixture of the aqueous liquor with a minor proportion of make-up water is intimately contacted with crude coke oven tar in .the proportion of 0.6-2.0 volumes aqueous mixture to one volume of crude coke oven tar, heating said mix-ture of tar and aqueous liquor to a temperature between and 350 F. under sufficient pressure Ito prevent substantial vaporization from the mixture, effecting separation of the mixture of heated coke oven tar and aqueous liquor into two phases by settling at a temperature within the range of 18o-350 F. under Sullicient pressure to prevent substantial vaporization into an aqueous layer and a tar layer, withdrawing the tar layer and subjecting it to reduced pressure to effect ash vaporization of a small amount of volatile aqueous constituents contained therein, discharging the flashed coke ture, effecting separation of the mixture of heated coke oven tar 'and aqueous liquor into two phases by settling at a temperature within the range of Z50-350 P. under suficient super-atmospheric pressure to prevent substantial vaporization into an laqueous layer and a tar layer, withdrawing the tar layer and subjecting it to reduced pressure to elect llash vaporization of a small amount of volatile aqueous constituents contained therein, discharging the flashed coke oven tar having a low concentration of arnmonium chloride and Water, .recirculating aqueous layer as aqueous liquor for further contact with crude heavy coke oven tar, discharging a small amount, about 10-20%, of the recirculating aqueous liquor, and introducing about l020% make-up water by volume of circulating liquor in admixture with the circulating aqueous liquor sucient to maintain the amount of circulating liquor substantially constant.

3. A process for the treatment of crude coke oven tar containing unseparated ammoniacal liquor, i.e. occluded aqueous liquor having dissolved therein ammonium chloride and phenolics, for reduction of ammonium chloride to below two pounds per 1,000 gallons of tar and of water to below 2% by volume of tar with concomitant production of an aqueous solution containing phenolics and ammonium chloride adapted for recovery of the phenolics and `ammonium chloride which comprises continuously recirculating aqueous liquor in a closed circuit in which a mixture of the aqueous liquor with a minor proportion of make-up water is intimately contacted with crude coke oven tar in the proportion of 0.620 volumes aqueous mixture to one volume of crude coke oven tar, heating 4said mixture of tar and aqueous liquor to a temperature between 180 and 350 F. under sucient pressure to prevent substantial vaporization from the mixture, effecting separation of the mixture of heated coke oven tar and aqueous liquor into two phases by settling at a temperature within the range of 180-350" F. under sufficient pressure to prevent substantial vaporization into an aqueous layer and a tar layer, withdrawing the tar layer andV subjecting it to reduced pressure to effect flash vaporization of a small amount of volatile aqueous constituents contained therein, discharging the liashed coke oven tar having a low concentration of ammonium chloride and water, condensing vapors evolved by said ashed vaporization of the tar,'returning said condensate for Contact with incoming crude coke oven tar, recirculating aqueous layer as aqueous liquor for further contact with crude heavy coke oven tar, discharging a small amount, about 5-25%, of the recirculating aqueous liquor,k and introducing about 5-25% make-up water by volume of circulating liquor in admixture with the circulating aqueous YVliquor sufficient to maintain the amount of circulating liquor substantially constant.

4. A process yfor 'the treatment of crude coke oven tar containing unseparated ammoniacal liquor, i.e. oc-

cluded aqueous liquor having dissolved therein ammonium chloride land phenolics, for reduction of ammonium chloride to below two pounds per 1,000 gallons of tar and of water to below 2% by volume of tar with concomitant production of an aqueous solution containing phenolics and ammonium chloride adapted for recovery of the phenolics and ammonium chloride which comprises sure to prevent substantial vaporization from the mixture, 25

effecting separation of the mixture of heated coke koven tar and aqueous liquor into two phases by flowing the mixture through a substantially horizontally disposed settling section and thence into a vertical settling sec tion by settling at a temperature within the range of 250 StilV 350 F. under sufficient superatmospherc pressure to prevent substantial vaporization into an aqueous layer and a tar layer, vwithdrawing the tar layer and subjecting it to reduced pressure to effect flash vaporization of a small amount of volatile aqueous constituents contained therein, discharging the flashed coke ovenAtar Y having a low concentration of ammonium chloride and water, passing vapors evolved by said flashed vaporization of the Star in indirect contact with crude coke oven feed tar to preheat said crude feed tar and to condense said vapors, returning said condensate for direct contact with incoming crude coke oven tar, passing aqueous layer in indirect heat exchange with incoming crude coke oven tar, recirculating said aqueous layer as aqueous liquor for further contact with crude heavy coke oven tar, discharging a small amount, about 10-20%, of the recirculating aqueous liquor, and introducing about 10-20% make-up water by volume of circulating liquor in admixture with the circulating aqueous liquor suicient to maintain the amount of circulating liquor substantially constant.

References Cited in the le of this patent UNITED STATES PATENTS 2,697,067 Reynolds Dec. 14, 1954 2,775,541 Karl Dec. 25, 1956 FOREIGN PATENTS Y 703,479 Great Britain -Feb. 3, 1954 

1. A PROCESS FOR THE TREATMENT OF CRUDE COKE OVEN TAR CONTAINING UNSEPARATED AMMONIACAL LIQUOR, I.E. OCCLUDED AQUEOUS LIQUOR HAVING DISSOLVED THEREIN AMMONIUM CHLORIDE AND PHENOLICS, FOR REDUCTION OA AMMONIUM CHLORIDE TO BELOW TWOI POUNDS PER 1,000 GALLONS OF TAR AND OF WATER TO BELOW 2% BY VOLUME OF TAR WITH CONCOMITANT PRODUCTION OF AN AQUEOUS SOLUTION CONTAINING PHENOLICS AND AMMONIUM CHLORIDE ADAPTED FOR RECOVERY OF THE PHENOLICS AND AMMONIUM CHLORIDE WHICH COMPRISES CONTINUOUSLY RECIRCULATING AQUEOUS LIQUOR IN A CLOSED CIRCUIT IN WHICH A MIXTURE OF THE AQUEOUS LIQUOR WITH A MINOR PROPORTION OF MAKI-UP WATER IS INTIMATELY CONTACTED WITH CRUDE COKE OVEN TAR IN THE PROPORTION OF 0.6-2.0 VOLUMES, AQUEOUS MIXTURE TO ONE VOLUME OF CRUDE COKE OVEN TAR, HEATING SAID MIXTURE OF TAR AND AQUEOUS LIQUOR TO A TEMPERATURE BETWEEN 180* AND 350*F. UNDER SUFFICIENT PRESSURE TO PREVENT SUBSTANTIAL VAPORIZATION FROM THE MIXTURE, EFFECTING SEPARATION OF THE MIXTURE OF HEATED COKE OVEN 